The present invention relates to papermaking fabric for use in the paper manufacture.
In the conventional papermaking process carried out by using a fourdrinier wire screen, a slurry of raw paper material is supplied onto a papermaking woven fabric or cloth running continuously in an endless manner. The papermaking cloth separates cellulosic fibers from the slurry to thereby form a moist paper web thereon. From this viewpoint, it can be said that the papermaking cloth functions as a filter in the process of forming the moist paper web. Mesh apertures of the fabric also referred to as the drain orifices serve for the function of separating water from the slurry. Further, in the case of a fourdrinier wire screen type papermaking machine, the papermaking fabric serves also as a driving belt and is thus subjected to a tension exerted by the machine. For this reason, it is required that the papermaking fabric should exhibit an enhanced runability.
Among the several requirements imposed on the papermaking process, the following are to be noted among others in connection with the papermaking cloth. Namely, the papermaking cloth is required to exhibit a high paper material retention, i.e. a minimum flow loss of the paper material, no generation of wire marks, a high drainage capability with a reduced water containing capacity, a high abrasion resistance capability, an enhanced runability and others.
With a view to satisfying the above requirements imposed on the papermaking woven fabric or cloth, there have heretofore been made a variety of proposals. However, at the present state of the art, there are yet unavailable the papermaking fabrics which satisfy the abovementioned requirements to the satisfactory extent.
By way of example, the papermaking cloth woven finely by using fine yarns in an effort to improve the paper material retention capability while preventing formation of the wire marks suffers from such shortcomings that the runability and the abrasion resistance capability are poor. In recent years, attempts have been made to form the papermaking surface of the fabric from the wefts to thereby improve the paper material retention capability. The papermaking surface formed from the wefts is certainly advantageous in that the cloth is improved in respect to the drainage property because of little or no possibility of the drain apertures existing between the warps being directly blocked by the paper material. In that case, it is however noted that the wire marks become more noticeable because the inter-weft gaps are increased correspondingly.
As an approach, it has already been proposed to increase the number of the wefts forming the papermaking surface of a double-weft woven fabric by disposing so-called floating yarns which are not ordinarily woven into the texture in the form of interweave with the warps and the wefts forming the cloth. This proposal is certainly an interesting technical concept from the standpoint of increasing the number of the wefts of the papermaking surface of the cloth, which concept cannot however be applied to practical papermaking process, because the wefts not woven into the texture, i.e. the floating yarns tend to be displaced and collected together under a hydraulic pressure applied thereto upon charging of the slurry on the papermaking cloth, resulting in that the papermaking surface cannot be maintained flat uniformly.
The problem of generation of the wire marks becomes more remarkable in the case of the single-layer woven fabric in which the wefts form projections on the papermaking surface.
There has also been proposed the use of a multi-layer woven fabric in an effort to realize a high drainage property and a papermaking surface of a fine mesh while ensuring a high abrasion resistance capability.
Recently, there arises also a trend that the papermaking process is carried out at a higher speed with a view to increasing the efficiency of papermaking process, which however presents additionally new problems. The multi-layer woven fabric which can certainly exhibit advantageous effects unattainable with the single-layer cloth has a high water containing property which is primarily ascribable to a large volume of voids. Consequently, there will take place at a high rotational speed such phenomenon that water contained in the cloth is caused to spill out at the locations of the rotating turn-back rolls under a centrifugal force.
In this conjunction, it is noted that the single-layer woven fabric is substantially insusceptible to the phenomenon mentioned above due to inherently small water retaining capacity. However, the single-layer woven fabric is disadvantageous in that the wire marks are likely to be generated, the paper material retaining capability is poor and that the yield of the papermaking is not to be satisfied, as described hereinabove.
In the course of intensive studies conducted by the inventor of the present application in tackling the solution of the problems associated with the requirements for a high paper material capability, suppression of generation of the wire marks, a high water drainage capability with a low water containing capacity, a high abrasion resistance capability and an improved runability and others, it has been found that an increased density of the wefts in the papermaking surface of fabric is not suited for enhancing the raw paper material retention capability, while the multi-layer woven fabric is subjected to a limitation in reducing the water containing capacity of the fabric, requiring thus the use of the single-layer woven fabric. On the basis of this recognition, the inventors have reached the present invention.